Field
The present invention relates to a level shift circuit and a drive circuit.
Background
Level shift circuits for shifting the level of a drive signal from a low-potential side to a high-potential side are used to drive a semiconductor switching device on the high-potential side in drive circuits such as inverter apparatuses. Generally, HVICs (High Voltage Integrated Circuits), photocouplers, micro-transformers or the like are used as such level shift circuits (for example, see Patent Literature 1: JP 2003-115752 A).
An HVIC is constructed of PN junction isolation and electrically transmits a signal using a semiconductor device such as a MOSFET. A photocoupler is constructed of a light-emitting device such as a light-emitting diode and a light-receiving device such as a phototransistor, and transmits an electric signal by converting it to light. A micro-transformer is constructed of a coil and transmits an electric signal by converting it to magnetism.
However, with the HVIC, since the high-potential side is not electrically insulated from the low-potential side, noise on the high-potential side may transmit to the low-potential side. Since the photocoupler has a 2-chip configuration including the light-emitting device and the light-receiving device, it is difficult to miniaturize the photocoupler. The micro-transformer is also constructed of a plurality of chips just like the photocoupler, and so the micro-transformer is not only difficult to miniaturize but also more expensive than the HVIC and photocoupler.